1. Field
The present invention relates to an imaging system for observation of micro objects with variable view and a method thereof, and more specifically to an imaging system for observation of three-dimensional micro objects and dynamic micro objects with variable zenith angle, azimuth angle and position of view and an operation method thereof capable of steering view parameters by controlling active optical elements, such as a scanning mirror, wedge prisms and a deformable mirror.
2. Description of the Related Art
With the development of the micro-electro-mechanical systems (MEMS) and biotechnology, there is a growing interest in observation of dynamic targets in three-dimensional (3D) space. However it is still very difficult due to many reasons. One of the important reasons is insufficient vision information using the traditional vision system with fixed optical parameters. Occlusion, low depth resolution and small field of view (FOV) are three main difficulties. In occlusion case, some important features are occluded by the object itself or other objects. Low depth resolution refers to the low reservability along the depth direction. The small FOV issue often occurs when the workspace is larger than the FOV of the optical system. Keeping the region of interest (ROI) on a moving target from the best view direction is critical for observation. Especially for the cases of microassembly and micromanipulation, the two-directional interaction between a micromanipulator/microrobot and a vision system is an important factor for the success of these applications. The vision system must adjust its optical parameters corresponding to the variation of the observed targets.
Although multiple fixed microscopes (Probst, M., Vollmers, K., Kratochvil, B. E. and Nelson, B. J., “Design of an Advanced Microassembly System for the Automated Assembly of Bio-Microrobots,” presented at 5th International Workshop on Microfactories, Besancon, France, 25-27, 2006) and moving stages (Hui, X., Weibin, R. and Lining, S. “A Flexible Experimental System for Complex Microassembly under Microscale Force and Vision-based Control,” Int. J. Optomechatronics 1, 81-102, 2007) are often applied, they are not suitable for general applications. Such approaches do not provide sufficient flexibility and calibrations for different configurations are required. With moving stages, both the manipulation and assembly systems need to be installed on the stage and move together to change the FOV. This also generates agitation in the specimen. Therefore, development of a smart vision system with adjustable optical parameters by integration of optical and robotics technologies will be a promising solution.
As one of these technologies, U.S. Patent Publication No. US 2007/0253057 A1, discloses “Adaptive-Scanning Optical Microscope (ASOM)”, which can steer a sub field of view in a large area through the integration of a scanning mirror and a scanning lens group. The wavefront error induced by the scanning lens group is corrected by a deformable mirror. It can be considered as a two degrees-of-freedom active optical system which has a variable view position.
Another active optical system was proposed, which can interact with the environment by changing optical system parameters such as the view position and orientation with four degrees-of-freedom in a compact manner (Korean Patent Application No. 10-0839871, “Variable View Active Optical System and Control of Deformable Mirror Surface Image for the Same”, Jun. 13, 2008). The system integrates a pair of wedge prisms, a scanning mirror, a deformable mirror and off-the-shelf optical elements. However, because of the coupling effect between the scanning mirror angle and view angle, the view angle also varies when the scanning mirror operates, which decreases the zenith angle of view and makes the kinematics complex. Because of the coupled Jacobian matrix, the singularity of Jacobian is difficult to identify. The numerical inverse kinematics algorithm is difficult to achieve a solution when the system is near the singularity configuration. The coupled design also makes the calibration of system difficult. The position error between the scanning mirror and the wedge prisms will cause a large error in view state.